Magnetostrictive device



Je 29, 1948. R L PEEK, JR 2,444,061

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Patented June 29, 1948 STATES PATENT GFFQE MGNETOSTRICTIVE DEVICEApplication May 26, 1944, Serial No. 537,503 11 Claims. (Cl. 177-386)`This invention relates to magnetostrictive devices and more particularlyto submarine signaling devices of the magnetostriction type.

One object of this invention is to simplify the construction ofmagnetostrictive devices and more particularly of magnetostrictive sonictransducers intended for operation in the audio frequency range.

Another object of this invention is to improve the emciency of submarinesignaling devices of the magnetostriction type.

in one illustrative embodiment of this invention, a submarine signalingdevice comprises a magnetostrictive bar mounted for free vibration inits fundamental exural mode and a signal coil electromagneticallycoupled to the bar for eiecting vibration thereof in accordance withsignal currents supplied to the coil or, conversely, for translatingvibrations of the ba'r into electrical signals.

In accordance with one feature of this invention, the magnetostrictivebar is polarized longitudinally and is provided adjacent its center witha transverse longitudinally extending slot whereby the central portionof the bar comprises two parallel arms polarized in the same direction.The signal coil lencompasses only one of these arms. When the barvibrates, as in response to forces due to compressional waves effectivethereon, one of the arms is placed under tension when the other is undercompression, and vice versa, so that the flux changes in the two armsare opposite in sign and a signal ilux traverses a series path throughthe portions of the bar surrounding the slot. Similarly, when signalcurrents are supplied to the coil, the flux changes produced in the twoarms are opposite in sign and the bar is caused to vibrate iiexurally.

In accordance with another feature of this invention, the bar issupported at the nodes of its fundamental exural mode by resilientmounts, whereby mechanical losses are reduced and improved emclency isrealized.

The invention and the above-noted and other features thereof will beunderstood more clearly and fully from the following detaileddescription with reference to the accompanying drawing in which:

Fig. l is a perspective view of a. magnetostrictive transducer unitillustrative of one embodiment of the invention;

Fig. 2 is a sectional view of a submarine signal.- ing device includinga transducer unit of the construction shown in Fig. l;

Fig. 3 is a side view. to an enlarged scale, of

. 2 l the core assembly included in the unit illustrated in Fig. l; and

Fig. 4 is a side view illustrating a modification of the unit shown inFig. 1.

Referring now to the drawing, the transducer unit illustrated in Fig. 1comprises a non-magnetic foundation member or supporting plate i0 havingaixed thereto, as by screws il as shown in Fig, 2, a pair of U-shapedsupports i2 having rounded bearing surfaces it. In one construction, thesupports l2 may be of magnetic iron and constitute pole-pieces of a barmagnet lli the ends of which are fitted in the supports.

Seated upon the bearing surfaces i3 and held thereon initially bymagnetic attraction is a magnetostrictive beam or bar l5 which, in aparticularly advantageous construction, comprises a plurality of thinlaminations insulated from one another and bonded together by animpregnating compound such as a phenolic condensation product. As shownmore clearly in Fig. 3, the beam or bar I5 is provided at its cen-4 tralportion with a transverse slot i3 so that this portion comprisessubstantially identical, longitudinally extending parallel arms Il andI8. A signal coil i9 is woun'd about the arm It.

The beam or bar i5 is polarized longitudinally by the magnet I li, thepolarizing ilux traversing the two arms Il and i8 in the same directionas indicated by the solid arrows on the core in Fig. 3. When the bar isflexed, as by compressional waves eiective thereon in the directionindicated by the arrow S in Fig. 3, the two arms are stressed inopposite sense, that is when the arm Il is placed under compression thearm IS is placed under tension. Hence, the iiux changes in the two armsdue to magnetostriction are opposite in sign and a circulating flux owsin the core around the slot IS, for example as indicated by the dottedarrows in Fig. 3, and a signal current is induced in the coil I9.Conversely, when signal currents are supplied to the coil I9, the fluxchanges in the two arms are opposite in sign so that one arm contractswhile the other expands and, -as a result, the bar is vibrated inaccordance with the signal currents.

The transducer unit is particularly suitable for operation as a singlefrequency device, that is one sharply resonant at a prescribedfrequency. In this case, the beam or bar length is made such in relationto the beam thickness that the fundamental exural mode corresponds tothe prescribed frequency and the supports l2 are so spaced that thecontact between. the bearing surfaces l and the beam or bar are eachsubstantially 0.22 times the length of the beam from the nearest end ofthe beam, whereby the magnetostrictive element is freely supported atits nodes for its fundamental ilexural mode. It will be appreciated thatfor such single frequency devices, relatively short cores may beemployed. For example, in a device intended for operation at 5kilocycles the core length is approximately 21/2 inches.

The unit illustrated in Fig. .1 may be used to particular advantage in asubmarine signaling device as shown in Fig. 2. The device shown in thelatter gure comprises a diaphragm 20, for example of metal, aixed to amounting ring 2l. The unit is secured -to the ring 2| by a plurality ofscrews 22 threaded into the ring and is spaced therefrom by other screws23 threaded into the plate lil and bearing against one i'ace of the ring2 l. The magnetostrictive core lli is coupled to the diaphragm 2i] by abody or block 2l, for example a block of a commercially available formof rubber having good compressional wave energy transmissioncharacteristics, aiilxed, as by cement, to the core. In the assembly ofthe device, the screws 23 are adjusted so that they will engage the ring2l only when the lblock 2l has been compressed to be in intimate contactwith ,the core and the diaphragm by tightening of the screws 22.

In a particularly advantageous construction. the beam or bar l5 is madeof a magnetic material having high remanence so that the beam or bar iscapable oi self-polarization and the magnet Hl may be omitted. Thesupports I2, in such construction, may then be of a resilient material,such as soft rublber, as illustrated in Fig. 4, suitably aixed to thefoundation plate lil. The beam or bar, in such construction, is held inposition between the supports l2 and the Iblock 24 when the plate IB issecuredto the mounting ring 2l. A special Ifeature of this constructionis that the beam is in effect oatingly mounted so that mechanical lossesare reduced and improved eiiciency is obtained.

Although speciiic embodiments of this invention have been shown anddescribed, it will be understood that they are but illustrative and thatvarious modications may be made therein without departing from the scopeand spirit of this invention as deiined in the appended claims,

What is claimed is:

1. A magnetostrictive device comprising a magnetostrictive bar polarized-longitudinally and having a transverse slot therein, extending normalto the thickness of said bar and dividing an intermediate portion onlythereof in-to a pair of longitudinally extending arms, means mountingsaid bar for flexura1 vibration in the direction of its thickness, and asignal coil in electromagnetic coupling relation with one of said arms.

2. A magnetostrictive device in accordance with claim 1 wherein saidmounting means comprises supports engaging said bar at the nodes of itsfundamental flexural mode.

3. A magnetostrictive device compris-ing a magnetostrictive fbar havinga transverse slot in its center portion dividing said portion into apair of longitudinally extending arms, means for polarizing said armsmagnetically in the same direction, means mounting said bar for flexuralvibration in the direction normal to said slot, and signal cc-il meansin electromagnetic coupling relation with one of said arms.

4. A magnetostrictive device in accordance with claim 3 wherein saidmounting means comprises supports engaging said bar at regionssubstantially 0.22 times the bar length from the ends thereof.

5. A magnetostrictive device comprising a longitudinally rpolarizedmagnetostrlctive bar having intermediate its ends, two longitudinallyextending, substantially coextensive spaced portions which together withportions adjacent thereto define a closed magnetic loop, resilientsupports engaging said bar at the nodes thereof for its fundamentalexural mode. means for flexing said lbar in the direction to vary thestresses in said two portions in opposite sense, said flexing meanscomprising a diaphragm coupled to said bar, and a signal coil inelectromagnetic coupling relation Iwi-th one oi said spaced portions.

6. Amagnetostrictive device comprising a magnetostrictive bar having apair of adJacent. spaced, longitudinally extending arms intermediate itsends and defining a closed magnetic path with portions of said baradjacent the ends of said longitudinally extending arms, means forpolarizing said arms in the same direction, a signal coil linked to oneof said arms. and means for stressing said arms simultaneously and inopposite sense.

'7. A magnetostrictive device comprising a magnetostrictive bar having apair of parallel longitudinally extending arms in the mid-portionthereof and dening a closed magnetic path with portions of said bar atthe ends of said arms, means for polarizing said arms magnetically inthe same direction, means mounting said bar for (free flexural vibrationin the direction to alter the stresses in the two arms in oppositesense, and a signal coil encompassing one of said arms.

8. A magnetostrictive device comprising a magnetostrictive bar having apair of parallel longitudinally extending armsin the mid-portion thereofand dening a closed magnetic path with portions of said -bar at the endsof said arms, means mounting said barat the nodes thereof for itsfundamental exural mode of vibra-tion in the direction lo stress saidarms in opposite sense, means fox polarizing said arms magnetically inthe same direction, a vlbratile mem- -ber coupled to said bar, and asignal coll in electromagnetic coupling relation with one of said arms.

9. A submarine signaling device comprising a magnetostrlctive bar havinga transverse slot therein dividing an intermediate .portion thereof intotwo longitudinally extending portions, a signal coil encompassing one ofsaid portions, a pair of spaced magnetic supports engaging said barbeyond opposite longitudinal extremities ci said intermediate .portionand mounting said vbar for flexural vibration in the direction to stresssaid longitudinally extending portions in the opposite sense, a magnetfor which said supports constitute pole-pieces, and a diaphragm coupledto said intermediate portion.

10. A submarine signaling device comprising a magnetostrictive barhaving a transverse slot in its mid-portion dividing said portion into apair of longitudinally extending arms, a. pair of magnetic supportsengaging said .bar at the nodes of its fundamental exural mode andmounting said rbar for exural vibration in the direction to stress saidarms in opposite sense, a permanent magnet extending between saidsupports, a signal coil encompassing one of said arms, and a diaphragmcoupled to said mid-portion.

11. A magnetostrictive device comprising a REFERENCES CITED Thefollowing references are of record in the file of this patent:

Number Number UNITED STATES PATENTS Name Date Rieker June 23. 1925 HayesJune 25, 1935 Christensen Aug. 18, 1936 Turner May 30, 1939 Lakatos July22, 1941 Turner Dec. 3, 1946 FOREIGN PATENTS Country Date Great BritainJuly 5, 1933 Great Britain Jan. 8, 1935

